Various types of polymeric substances such as polyethers have been industrially produced. Usually, these polymeric substances are produced by purifying a polymeric substance containing impurities (crude polymeric substance) to remove the impurities.
Examples of the impurities contained in such a crude polymeric substance include metal compounds derived from an alkali metal compound and a double metal cyanide complex, and specific examples thereof include the following compounds:    (1) In producing a hydroxyl-group-containing polyether by allowing an alkylene oxide to react with an initiator, a double metal cyanide complex catalyst is used as a catalyst. This catalyst remains in the resulting polymeric substance without change or as a modified decomposition product.    (2) When an oxyalkylene polymer such as polypropylene oxide is produced by addition polymerization of an alkylene oxide, an alkali metal compound such as sodium hydroxide or potassium hydroxide is used as a catalyst. This alkali metal compound remains in the resulting polymeric substance without change or as a salt.    (3) When a functional-group-containing polymer such as an oxyalkylene polymer or a diene polymer that has a hydroxyl group or a carboxyl group is allowed to react with a halogen-containing compound such as epichlorohydrin or allyl chloride to produce a polymer having another functional group, an alkali metal compound such as sodium hydroxide or potassium hydroxide is used as a catalyst. This alkali metal compound remains in the resulting polymeric substance without change or as a salt.
In addition to the above cases, there are many crude polymeric substances contaminated with a metal compound such as an alkaline earth metal compound or a transition metal compound.
Since such a metal compound remaining in a polymeric substance causes various problems, the metal compound is preferably minimized. For example, when the polymeric substance is used in further reaction, the metal compound may affect the reaction rate or the reaction yield. Therefore, the metal compound must be sufficiently removed. More specifically, when methyldimethoxysilane or the like is allowed to react with an allyl-group-terminated polyether in the presence of a platinum-containing catalyst, a metal compound remaining due to insufficient removal significantly decreases the reaction rate.
In general, impurities are often removed by, for example, a treatment with an adsorbent or a method including neutralization, filtration, and subsequent extraction with water.
Among these, the treatment with an adsorbent is disadvantageous in that the treatment is not suitable for treating a large amount of metal compound and that the type of usable adsorbent is limited when the metal compound is a salt.
The method including filtration is disadvantageous in that crystals of neutralized salts must be enlarged and that the salts are dissolved in water when water is present.
Because of these problems and other reasons, a method of extraction separation is suitable for many cases.
The method of extraction separation is a method of sufficiently bringing a crude polymeric substance into contact with water to transfer a metal compound in the form of a water-soluble salt to the water, and then separating the water from the polymeric substance. Hitherto, it has been believed that when vigorous agitation is performed in order to satisfactorily bring a crude polymeric substance into contact with water, the system easily becomes an emulsion state because of the presence of the polymeric substance (Patent Documents 1 and 2). In particular, Patent Document 2 describes as follows: “Since polyethers produced in the presence of a double-metal cyanide complex catalyst are emulsified with water very easily, it is extremely difficult to remove the catalyst by an extraction method”. Accordingly, it may take a long time for the subsequent separation of water from the polymeric substance or a huge apparatus may be required. On the other hand, when the agitation is moderately performed to prevent emulsification, the metal compound is not satisfactorily extracted. Consequently, it is necessary to establish a technique that satisfies incompatible conditions, namely, a technique in which the extraction efficiency is increased and the separability is also increased. Furthermore, such an extraction method using water cannot be used for polymeric substances having high hydrophilicity. Even in hydrophobic polymeric substances, when a trace of hydrophilic impurities is contained in starting materials, emulsification occurs extremely easily. Accordingly, the application of such an extraction method is significantly limited for industrial use. It is desirable to establish a production method including a versatile purification method that can be used for not only unsaturated-group-containing polyethers but also high-molecular-weight polyethers having the above properties.
An example of a disclosed method is a method including centrifugal separation to actively promote oil-water separation (Patent Document 3). As an apparatus used for a general method of extraction separation, a spray tower; a continuous countercurrent extraction tower, such as a stirring-type tower, and a reciprocating-type tower; and a centrifugal separator are used and disclosed (Patent Documents 1 and 3). These unexamined patent applications provide a method in which a polyether, which is a polymer, and water are agitated in a high-speed-agitation-type agitation tank equipped with impellers, and the water phase is then separated from the polyether phase in a centrifugal separator or a countercurrent contact-type agitation tower or using a filter. However, in these methods, in order to increase the extraction efficiency, an agitation tank for high-speed agitation and an expensive centrifugal separator or a filter must be used. It is believed that this is a problem to be solved.
Furthermore, when a polyalkylene oxide is produced by ring-opening polymerization of an alkylene oxide having three or more carbon atoms, such as propylene oxide, and an initiator contains a polymer of ethylene oxide or the monomer contains ethylene oxide as an impurity, these components increase the hydrophilicity of the resulting polymer, and thus it may be significantly difficult to perform extraction separation with water. In order to prevent this problem, it is necessary to strictly control the content of the polymer of ethylene oxide in the initiator and the content of ethylene oxide in the monomer.    Patent Document 1: Japanese Unexamined Patent Application Publication No. 2002-249580    Patent Document 2: Japanese Unexamined Patent Application Publication No. 8-231707    Patent Document 3: Japanese Unexamined Patent Application Publication No. 1-294733